The use of trichloromonofluoromethane in the production of closed cell, rigid polyurethane and polyisocyanurate foams is well known (see, e.g., U.S. Pat. Nos. 3,072,582; 3,091,551; 3,153,002; 3,524,825; 3,846,347; and 4,248,975). Recently, the urethane foam industry has been investigating methods for reducing the amount of trichloromonofluoromethane used in producing rigid foams.
U.S. Pat. No. 4,448,951 broadly suggests the use of methyl formate as a blowing agent in the production of rigid foams. U.S. Pat. No. 4,033,910 broadly describes the use of a mixture of methyl formate and 1,1,2-trichloro-1,2,2-trifluoroethane in the production of phenolic foams.
U.S. Pat. No. 3,745,203 describes the production of polyurethane moldings using a mixture of two volatile blowing agents. The least volatile of the blowing agents has a boiling point of from 30.degree. F. to 120.degree. F., while the more volatile blowing agent in the mixture has a boiling point of from -50.degree. F. to 50.degree. F. The difference between the boiling points of the two blowing agents in the mixture is from 30.degree. F. to 150.degree. F. Specific mixtures described include methyl formate and either dichlorodifluoromethaneor dichlorotetrafluoroethane.
U.S. Pat. No. 3,879,315 describes the use of a mixture of a fluorocarbon (and, specifically, trichloromonofluoromethane) and an alkyl alkanoate having a molecular weight of 74 or less (such as methyl formate) in the production of flexible polyurethane foams.
DuPont has a commercially available blowing agent, known as Freon 11H, which is a blend of methyl formate and trichloromonofluoromethane. Freon 11H has been marketed by DuPont for use in the preparation of flexible polyurethane foams (see, brochure entitled "DuPont Freon Fluorocarbons . . . High Performance Blowing Agents").
Finally, the use of dichlorotrifluoroethane above, and in combination with trichloromonofluoromethane, for producing polyurethane foams is known (see, e.g., U.S. Pat. Nos. 4,076,644 and 4,624,970).